sGray Profile

AS
Posted By
Alan Smithee
Aug 23, 2005
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779
Replies
4
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Closed
What is the sGray profile used for under color settings Working Spaces | Gray ?

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TA
Timo Autiokari
Aug 24, 2005
"Alan Smithee" wrote:

What is the sGray profile used for under color settings Working Spaces | Gray ?

It is grayscale working-space profile that has the same transfer function that the sadRGB RGB working-space profile has.

It is sensible to use such a grayscale working-space profile that has the same transfer function that the current RGB working-space profile has. Othervice e.g. the individual channel views are not corect.

TImo Autiokari
http://www.aim-dtp.net/
AS
Alan Smithee
Aug 24, 2005
Timo Autiokari wrote:
"Alan Smithee" wrote:

What is the sGray profile used for under color settings
Working Spaces | Gray ?

It is grayscale working-space profile that has the same transfer function that the sadRGB RGB working-space profile has.

What’s sadRGB? By transfer function you mean a curve or like the transfer function in the print dialogue?
It is sensible to use such a grayscale working-space profile that has the same transfer function that the current RGB working-space profile has. Othervice e.g. the individual channel views are not corect.

So in practical terms how do I use it? With RGB images that I want to convert or work on in Black & White?

TImo Autiokari
http://www.aim-dtp.net/

Thx.
BH
Bill Hilton
Aug 25, 2005
What’s sadRGB?

sRGB … while officially "s" stands for "standard" (at least HP and Microsoft wish it were standard) to Timo and many others used to wider spaces it can also signify "sorry", "sad", "small" or "shi**y 🙂
TA
Timo Autiokari
Aug 25, 2005
Alan Smithee wrote:

By transfer function you mean a curve or like
the transfer function in the print dialogue?

Yes, due to historical technical reasons many RGB spaces are non-linear, namely they have transfer function that has the form of a power function, it is also called as gamma. Gamma 2.5 is the transfer function of the CRT monitors. In Mac systems the image data is by default adjusted by the operation system by gamma 1/1.45 so the effective gamma of Mac systems with CRT monitor is 2.5*(1/1.45)=1.72 but due to a fault in a historical tool (The Mac gamma tool) it was said to be 1.8. The very same fault (by the very same author) was there in the Gamma tool that the Windows version of Photoshop had up to v
4.0.1, therefore the gamma in default PC systems is said to be 2.2
while it in reality is gamma 2.5 since Windows operation systems by default do not adjust the data that goes to monitor at all.

sadRGB (sRGB) has a transfer function that is not a gamma gamma function, this has the effect that there will be more color error when the image is edited sadRGB color-space than what there are when the image is edited in an accurate gamma 2.2 color-space. sadRGB has the gamut (primaries or phosphors set) named as the HDTV, there are no display systems that have these primaries, the vast majority of CRT monitor have primaries that have the name Trinitron (this does not have anything to do with the mask technology that also is called as Trinitron). Due to this gamut issue sadRGB images that you see on the Web often have slight reddish or magentaish cast. So, sadRGB really is not good at all for Web publishing.

So in practical terms how do I use it? With RGB images
that I want to convert or work on in Black & White?

Photoshop is automatically using the current RGB and grayscale working-space profiles. So when you convert from RGB to Grayscale then it is converted from the current space that the image has to your grayscale working-space profile. Also the individual channel views are shown using that gray profile.

If you work in an other RGB working space than the sadRGB then it is sensible (necessary) to change also the Gray working space profile,
e.g. if you work in a linear RGB working space then open the
Edit/ColorSettings dialog, there open the Working Spaces Gray dropdown, select the second item from the top of that list (Custom Gamma) and enter the value 1.0 to that dialog. If you insist to work in a non-linear RGB working-space like the adobeRGB then do the above but enter the value 2.2 to the custom gamma dialog.

Timo Autiokari
http://www.aim-dtp.net/

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